Glaucoma, a disease generally caused by rise in blood pressure in the eye, gives damage to the visual nerve system, leading to a symptom of loss of vision. Various medical products have been developed and put into use as therapeutical agents for this glaucoma. In research and development of medical products in general, not limited to those of the therapeutical agents for glaucoma, an efficacy test of the agent using animals as subjects is essential before it is put for use in a clinical test. Since glaucoma is a disease leading to loss of vision as described above, it is preferred that such efficacy test be effected in the form of determination of visual field. However, it is extremely difficult to conduct determination of visual field with high accuracy with using an animal subject. Therefore, in actuality, the efficacy test has been conducted not in the form of determination of visual field, but in the form of determination of ophathalmotonometry (eye blood pressure).
On the other hand, as an instrument for determining visual field, a Humphrey field analyzer is usually employed. This field analyzer was developed for determining visual field of human. In its use, a subject is seated in front of an eye target display screen and instructed to fix his/her eye on a gazing point illuminated at a substantially center position in the eye target display screen. Under this condition, an eye target is illuminated at a predetermined position in the eye target display screen, and when the subject recognizes this illumination, the subject shows it by e.g. pressing a response button. During this determination, the subject assumes a posture with his/her chin placed on a fixing platform for fixing the subject's head.
As described above, in the research and development of a therapeutic agent for glaucoma, the determination of visual field has an important roll. Hence, there has been a need to develop a technique which allows an efficacy test to be conducted by way of visual field determination using an animal subject. It is known that there exists close correlation of central cavity visual function between the human and the monkey. Then, if the determination of visual field with using a monkey is made possible, this will help deduce the efficacy of the agent in a human subject with higher accuracy, thus being very useful for the research and development of therapeutic agent for glaucoma.
However, the above-described Humphrey field analyzer was developed for determination of visual field of humans. So, although this instrument can be appropriately used when smooth communication is possible between the operator and the subject, it is difficult to use this for determination of visual field of a money with which communication is not easy.
Further, in the determination of visual field, it is determined to which level of illumination the subject can recognize each position in his/her field of vision. The greater the number of points determined and the greater the number of levels of brightness determined at the respective points, the higher the accuracy of the measurement result. However, in the case of the Humphrey field analyzer, considering the time period when a human subject can keep his/her concentration in the determination, the instrument is designed so that the determination is completed in a short period of time. Therefore, it is not possible to determine a threshold value with varying the brightness in small increments or to conform the reproducibility of the determined values. In this respect, the instrument is not satisfactory in terms of the accuracy of the visual field determination.
For this reason, there has been a need for developing a system and a method which allow accurate determination of visual field of a monkey. In addition, since the Humphrey field analyzer is expensive, there has also been a need for a less costly determining system utilizing a general-purpose instrument.
An object of the present invention is to provide a system and a method for determining visual field of a monkey, which allow high accuracy determination of visual field of a monkey just like that of a human subject.